1. Field of the Invention
The present invention relates to an optical projection device. More particularly, the present invention relates to a dust protection device for the optical projection device.
2. Description of Related Art
In general, conventional optical projection device is mainly constructed by light source, imaging unit and projection lens. The imaging unit includes a non-direct view display device such as silicon-based liquid crystal panel, high temperature polycrystalline silicon liquid crystal panel or digital micromirror device (DMD), and an optical lens set constructed by reflection mirrors and lens. The light source is adopted for providing a light beam into the imaging unit. The optical lens set is adopted for transmitting the light beam into the display device. The display device receives the light beam and generates an image, and then the image is transmitted to the projection lens via the optical mirror set. Finally, the image is projected to a projection screen by the projection lens.
In general, the resolution of the display device optical projection device has high resolution. The higher image quality of the projected and the enlarged image can be achieved. However, it is noted that the image is enlarged several times in the optical projection device. Therefore, if the display device or the optical lens set is covered with dust or other contaminations, the display device is damaged. In addition, the interference due to the dust or the contaminations is also simultaneously enlarged with the image during being projected to the projection screen. Therefore, the quality of the image displayed is adversely affected.
Accordingly, a dust protection device is developed for the internal optical lens set and the display device in a conventional optical projection device. FIG. 1A is a perspective view of a conventional optical projection device. FIG. 1B is a top view of the optical projection device shown in FIG. 1A. It is noted that, parts of the housings are shown in FIG. 1B. Referring to FIG. 1B, the projection lens 130 is mounted on the housing 110. The terminal of the projection lens 130 is connected to a barrel (not shown), thus the terminal of the projection lens 130 cannot be lengthened or shortened. A DMD 122 and an optical lens set are installed in the housing 110, wherein the optical lens set generally includes a relay lens 124 and other optical lens (not shown). Generally, in order to protect the DMD 122 from the dust or the contaminants, conventionally the relay lens 124 is installed outside of the DMD 122 and over the projection lens 130. Therefore, the DMD 122 is surrounded and sealed by the relay lens 124 and the barrel for mounting, so that the DMD 122 is protected from dust.
However, as the demand of the display quality and the magnifying power of the image increase gradually, the size of the projection lens is also increased. For this reason, the optical path among the projection lens is also lengthened. Therefore, the terminal of the projection lens cannot be mounted in the barrel, and thus the relay lens and barrel cannot be sealed from the dust. In summary, the conventional optical projection device cannot be adopted for high magnification projection lens. In addition, the conventional dust protection mechanism has to be modified corresponding to the development of optical system.